The selective recovery of specific materials from chemical solutions is a problem addressed in various ways depending on the application or process involved. In the case of plating processes, it is desirable to, at the very least, remove metal ions from the various rinse waters that are carried from the plating tank or tanks by the product being plated. Environmental concerns mandate that potentially harmful materials be removed from the effluent of these processes prior to discharge as waste. It is also desirable to recover and reuse the metal ions themselves for return to the plating tank. In this way material is conserved while at the same time preventing these materials from being discharged into the environment.
Methods and apparatus for removing or recovering metal ions from rinse baths have been suggested in the past. In one suggested application, the rinse water is passed through an ion exchange resin which captures the metal ions. During a "regeneration process", the ion exchange resin releases captured ions and the regeneration solution along with the released ions is conveyed to the metal plating bath. Unfortunately, in many if not most methods, the ion exchange resin captures all the ions having a common polarity. In the case of a nickel plating process, an ion exchange vessel designed to capture nickel ions will also capture various alkali metal ions and alkaline earth metals such as sodium, potassium, calcium and magnesium. When the resin is regenerated, the solution including all of the desirable (nickel) and undesirable (sodium, potassium, calcium, magnesium) ions are returned to the metal plating bath. Consequently, the overall contamination level (caused by the presence of the alkaline metal ions) increases in the tank. Eventually, the plating solution may require added purification steps or be partially or completely replaced in order to lower the concentration of contaminants.
In an effort to obviate this problem, it has been suggested that the regeneration solution containing the ions be further processed by other methods and apparatus in order to selectively recover the desired metal ion. This extra processing and additional apparatus increases the overall costs of the plating operation and is considered unacceptable by many metal plating operators.